Partners' Capital, Equity and Incentive Compensation Plans (Summary of Assumptions and Fair Values for Restricted Stock and Options to Purchase Shares of Class A Common Stock Granted) (Details) - $ / shares	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected volatility		33.00%
Expected dividend yield		3.57%
Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair value of restricted stock granted	$ 45.78	$ 35.81
Fair value of options granted	$ 9.57	$ 8.00	$ 4.94
Expected term (years)	5 years 6 months	5 years 6 months	5 years 6 months
Expected volatility	30.70%		33.00%
Expected dividend yield	3.14%	3.40%	4.02%
Expected risk-free interest rates	1.42%	1.67%	1.70%
Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair value of restricted stock granted	$ 56.28	$ 37.69
Fair value of options granted	$ 9.97	$ 8.77	$ 5.98
Expected term (years)	5 years 10 months 24 days	6 years 1 month 6 days	6 years 1 month 6 days
Expected volatility	31.30%
Expected dividend yield			4.55%
Expected risk-free interest rates	1.48%	1.94%	1.90%